NU FS 372+373
Key concepts
Remember common functional groups and be able to recognise them in complex organic molecules (slides 3-12)
Understand the concepts of electronegativity and polarity
Understand the principles governing solubility and miscibility
Be able to define log Pow and understand the singificance of log Pow values
Alkanes: CnH2n+2
Formula | Structure | Name / Uses | |
CH4 | Methane - gas used for cooking. | ||
C2H6 | Ethane | ||
C3H8 | Propane - heating fuel. | ||
C4H10 | Butane - lighter / camping fuel. | ||
C5H12 | Pentane | ||
C6H14 | Hexane |
Hydrocarbon Rings:
Formula | Structure | Name / Uses | ||
C6H12 | Cyclohexane - a saturated hydrocarbon with the atoms arranged in a hexagonal ring. In organic chemistry, the presence of Hydrogen atoms is often assumed and this compund can be reprsented by a hexagonal ring: | |||
C6H6 | Benzene - an industrial solvent. The Benzine Ring is one of the most important structures in organic chemistry. In reality, its alternate double and single bonds are "spread around" the ring so that the molecule is symetrical. This structure is represented by a hexagon with a circle: | |||
C7H8 | Toluene - an important solvent and starter chemical. Using the Benzine Ring, this molecule can also be depicted as: | |||
C10H8 | Naphthalene - used in moth balls. This can be depicted as two fused Benzine Rings: |
Alcohols: CnH2n+1OH
eneral ormula | Series Name | Details | Examples | Structures | |||
CnH2n+1OH | Alcohols | Alcohols have the OH (hydroxyl) group in the molecule. | CH3OH Methanol wood alcohol C2H5OH Ethanol drinking alcohol C6H5OH Phenol carbolic acid - used as disinfectant |
Ethers: (CnH2n+1)2O
(CH3)2O | ||||||
Dimethyl | ||||||
Ethers have an O atom | Ether a gas | |||||
(CnH2n+1)2O | Ethers | attached to two hydrocarbon chains (or rings). | (C2H5)2O Diethyl Ether a liquid | |||
used as an | ||||||
anaesthetic) |
Aldehydes - CnH2n+1CHO
CnH2n+1CHO | Aldehydes have a CHO group attached to a hydrocarbon chain (or ring). | HCHO H Formaldehyde preservative in C labs O CH3CHO Acetaldehyde | H |
Ketones - (CnH2n+1)2CO
(CnH2n+1)2CO | Ketones have a CO group attached to two hydrocarbon chains (or rings). | CH3COCH3 Dimethyl Ketone Also known as acetone: nail- varnish remover |
Carboxylic Acids
C2H5CO2H
(fatty acids for high n): CnH2n+1CO2H
CnH2n+1CO2H | Fatty Acids contain the CO2H (or COOH) group attached to a hydrocarbon chain or ring. | HCO2H Formic Acid in ant bites and stinging nettles CH3CO2H Acetic Acid vinegar C3H7CO2H Butyric Acid the rancid butter smell | H3C |
Esters:
RCO2R’
RCO2R' (R, R' are Hydrocarbon chains or rings). | Esters are similar to Fatty Acids except that the H in the COOH group is another hydrocarbon chain. They are usually very sweet smelling liquids used in perfumes. | CH3CO2CH3 Methyl Methoate essence of pear drops |
Amines: RCH2n+1NH2
Amines have one or more of the Hydrogen atoms in Ammonia (NH3) replaced by a Hydrocarbon chain or ring. | ||||
CnH2n+1NH2 | Primary Amines have the formula RNH2 Secondary Amines have the formula RR'NH | CH3NH2 Methylamine a pungent, water soluble gas | ||
Tertiary Amines have the formula RR'R''N. | ||||
(R, R', R'' are Hydrocarbon chains or rings). |
Amino Acids H2NRCO2H
CnH2nNH2COOH | Amino Acids have two functional groups: the amine (HN2) group and the fatty acid (COOH) group. Amino Acids combine together to form proteins which are an important component of living organisms. | CH2NH2COOH Glycine the simplest amino acid. |
Amides: RCONH2
Primary Amides
propanamide
,
,
Benzamide
Secondary Amides - have one hydrogen and one alkyl or aryl group on the N of the amide group.
N-methylethanamide,
Tertiary Amides - have two alkyl or aryl groups attached to the N of the amide group.
N,N-dimethylethanamide,
,
POLYAMIDES are secondary amides formed in a condensation reaction between a carboxylic acid and an amine.
-COOH + H2N- -CO-NH- + H2O
POLYPEPTIDES (proteins) are polyamides formed between amino acids
(a “dipeptide”)
Visible spectrum
methyl
aldehyde
pyrrole
ethyl
ketone
ester
alkyl chain
Covalent bonds –
sharing pairs of
electrons. Single or H
N
H
multiple. Number of H
covalent bonds
dependent on valency
Ionic bonds – between O
H H C C
H H
strongly electronegative and electropositive atoms eg. salts
R C O-Na+
Na+Cl-
Electronegativity
Electronegativity is the attraction of an atom for the electron cloud that forms the bond between 2 atoms
Least electronegative element
Pauling Scale
Most electronegative element
Arises through differences in electronegativity:
★
A ★ B
δ+ ★ δ-
A ★ B
A and B have equal electronegativities..
nonpolar bond
+
A
B is more electronegative than A..
polar bond
★-
★B
B is much more electronegative than A..
ionic bond
B is more electronegative than A:
δ+ δ-
d
A B
The product of the magnitude of the charge (δ) either on A or B and the AB bond length (d) is called the dipole moment (µ) of the bond:
µ (AB) = δ x d (SI units are debye (D))
Molecular dipole moments are the vector sum of the dipole moments of all bonds in the molecule
H H
H C C H
H H H C C
H
OH
H H H H
Ethane: Non-polar Ethanol: Polar
Functional groups can be classified as electron withdrawing (−I) or electron donating (+I) groups relative to hydrogen
δδδδ+
δδδ+
δδ+
δ+
An electronegative (electron withdrawing) element X not only polarizes the C-X bond but also draws electrons away from more distant bonds to a diminishing extent. This is the inductive effect, occurring through σ bonds.
CH3——CH2——CH2——CH2——X
δ-
<
<
<
<
O2N—<<—CH2—<—Ph
H——CH2——Ph
NO2 is –I i.e. electron withdrawing; this also draws electrons away from the Ph group in the C--Ph bond
H
O δ-
Ion-Dipole – responsible for salts dissolving in water
r
δ-
δ+
hydrogen bonds
Hydrogen Bond (dipole-dipole) – between two pola molecules
R C O- δ+
O
H
O
Na+ δ-
H
H
-
+
-
+
Van der Waals Forces – induced or temporary dipole occurring as non- polar compounds
approach each other F
– a type of dipole- dipole interaction.
Dielectric constant (ε): A measure of a substance’s ability to insulate opposite charges from each other.
As a measure of solvent polarity, higher ε = higher polarity, greater ability to stabilize charges.
(In physics, dielectric constant is also known as permittivity or relative permittivity referring to the ability of a substance to attenuate the transmission of an electrostatic force from one charged body to another, compared to a vacuum for which ε = 1)
ε > 15 = polar solvent
ε < 15 =nonpolar solvent
Non- polar
Polar aprotic
Polar protic
Longer hydrocarbon chain less polarity
**
**
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Miscibility of Solvents with Water
http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Solvents_Site_Map.html
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** **
Miscibility of Solvents with Hexane
http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Solvents_Site_Map.html
Solubility of Alcohols[ CnH2n+1OH ]
R-OH | Boiling Point °C | Solubility g/100g Water |
Methanol | 65.5 | ∞ |
Ethanol | 78.3 | ∞ |
1-Propanol | 97.0 | ∞ |
2-Propanol | 82.4 | ∞ |
1-Butanol | 117.2 | 7.9 |
1-Pentanol | 137.3 | 2.3 |
Solubility of Carboxylic Acids
O R= R C OH | Boiling Point °C | Solubility g/100g Water | Solubility g/100g Ethanol |
H | 101 | ∞ | ∞ |
CH3 | 118 | ∞ | ∞ |
CH3-CH2- | 141 | ∞ | ∞ |
CH3-(CH2)2- | 164 | ∞ | ∞ |
CH3-(CH2)3- | 187 | 3.7 | Soluble |
CH3-(CH2)4- | 205 | 1.0 | Soluble |
C6H5- | 250 | 0.34 | Soluble |
CH3-(CH2)10- | Insoluble | 100 | |
CH3-(CH2)16- | Insoluble | 5.0 |
A
B
Solvents are H2O and CCl4 Density of CCl4 is 1.59 g/cm3
Solutes are I2 and KMnO4
Which solvent is the upper layer?
Which flask has I2 added ?
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch15/solut.php
How will the (coloured) compounds partition?
Oil/vinegar mixture
Herb infused oils
The partition (or distribution) coefficient is the ratio of the concentrations of a compound in two immiscible solvents at equilibrium
– ie. it is a measure of the difference in solubility of the compound between these two solvents.
Often the hydrophobic solvent octanol and water are used.
[solute]octanol
[solute]un-ionized
water
logPow is a measure of hydrophobicity (or lipophilicity):
log Poctanol/water
= log
(note: log10(10)=1; log10(1)=0; log10(0.1)= -1; etc)
Compound | log Pow |
Methanol | -0.77 |
2-Propanol | 0.5 |
1-Hexanol | 2.03 |
Benzene | 2.13 |
Limonene | 4.57 |
PCDD/PCDF (polychlorodibenzo- dioxin/furan) | 6.5-8.8 |
CH3
1.87 2.26 3.5 5.1
INCREASING experimental log P values >>>>>>>>
2.13 -1.85 -1.76 -3.24
DECREASING experimental log P values >>>>>>
Soluble in what ??
Solubility of CO2 in water
Figure 5–Fraction of dissolved carbon dioxide, carbonic acid, bicarbonate, and carbonate in water, as a function of pH (adapted from Daniels and others 1985).
Solubility of CO2 in a can
Henry’s Law:
The solubility of a gas in a liquid is proportional to the pressure of gas above that liquid
Picture from Chemistry Structures of Life, K.Timberlake, 2010
Simple Method for Measurement of CO2 in a food
Figure 6–Example of experimental set-up to measure carbon dioxide content in liquid or solid food, and associated reactions (adapted from Gill 1988).
Measurement of O2 also possible (eg using luminescence sensors) but interactions with the food must be considered)